Field of the Invention
This invention relates to a valved conduit for connecting a pressure fluid source to a fluid motor and more particularly to a device which is responsive to abnormal flow conditions such as heavy or light leakage downstream of the valve to shut off the flow of pressure fluid through the conduit.
Prior Art
Such devices are useful in oil-hydraulic systems where hydraulic liquid under high pressure is conveyed from a pump or other pressure fluid source to a working cylinder or other fluid motor through a hose or other conduit exposed to danger of becoming damaged. Such systems may be embodied in, for example, a digger, a loader or other construction or working machine having arms or other movable elements actuated by fluid motors into and out of which hydraulic liquid is conveyed through hoses.
In such systems, the high pressure of the hydraulic liquid in combination with the stresses to which the hoses are otherwise subjected can easily cause the hoses to leak, so that the hydraulic liquid starts escaping in an uncontrolled manner. If the leak is not immediately discovered and sealed, the escaping hydraulic liquid may rapidly cause severe damage. If a hose should burst or break and the supply of hydraulic liquid to the hose is not immediately shut off, there is, in addition to environmental damage caused by the escaping hydraulic liquid, a substantial risk of serious personal injury or damage to equipment.
It is known in the art to provide hydraulically operated machine components with so-called excess-flow safety valves which serve to prevent uncontrolled escape of hydraulic liquid and accidents in case a hose should burst or break. Excess-flow safety valves of the conventional type may function well if the hose is broken or bursts and also in other instances in which the leakage is very large, namely, larger than the largest flow the valve has to pass during normal operation. On the other hand they are not capable of also providing reliable protection in the not uncommon case of a smaller leakage, e.g. as caused by a minor crack or pinhole in the hose. Even small leakages may rapidly cause severe damage, however, and an excess-flow safety valve therefore should be reliably actuated in response to a relatively small leakage as well.